gas - 254 questions
natural-gas - 95 questions
propane - 59 question
Is there enough variance for this tag? Should we retag to the specific natural gas or propane tags?
I think gas makes sense for many questioners/searchers. They often know they are dealing with gas, but may not know which type.
I think you could try to retag some if its absolutely clear what they mean, but I would wager that most of them are not specific enough.
Adding a more specific tag in to help future searchers is good, but I agree that the generic [gas] tag is required.
I would point out that in some countries "gas" is the only term people would use to describe what others would call natural gas and or propane because gas is not a shorthand for gasoline. Some people would never tag propane or natural gas as its not a term they would ever be familiar with.